The invention relates to disk drives and storage medium devices, and more particularly to velocity control for disk drive actuators.
A conventional disk drive comprises an actuator for positioning a set of read and write heads over an associated set of data storage disk surfaces. During a typical power off occurrence whether by user design or a sudden loss of power, it is desirable to provide ahead retraction method to safely move the heads off of their associated disk surfaces to prevent damaging the disk surfaces and causing data loss resulting from head-to-disk surface contact. Moreover, the head retraction method must be functional under a reduced-power or power loss condition. In prior head retraction methods, during a power loss, the energy from the rotational mass of the rotating disks is converted by the spindle motor coupled to the disks into back electromotive force (EMF) and applied directly to a voice control motor (VCM) that drives the actuator transporting the heads. However, since the ramp loading and unloading reliability is a critical function of the velocity of the VCM as the actuator moves near and across a head ramp, providing accurate control over all VCM velocities is essential to maximizing the reliability of the head ramp unload or load operations. There is therefore a need for an efficient means of controlling the VCM velocities during the ramp load and unload process.
The invention resides in a velocity control method for ramp unloading of heads off of a disk in a disk drive. The method includes providing a VCM settling period for measuring the VCM velocity, and in response to the measured VCM velocity, controlling an applied VCM current to maintain the VCM velocity between a rninimum velocity and a maximum velocity.